The present invention relates to an exhaust support system for use in a midship engine rear wheel drive-type vehicle, and more particularly to an exhaust support system located between a vehicle body and an exhaust device such as a muffler or an exhaust pipe.
In general, a midship engine rear wheel drive-type vehicle, as shown in FIG. 1, is installed with an engine 3 located between a rear axle shaft 1 and a passenger seat 2. In such a vehicle, a nearly equivalent load is exerted on a front axle shaft 4 and the rear axle shaft 1. Hence, the steering control of this vehicle is superior to the steering control of other types of vehicles, resulting in midship engines being installed in many sports cars. To further improve the performance of the steering control in sports cars equipped with midship engines, the lengths l.sub.1 and l.sub.2 of a front overhang and a rear overhang 5 and 6, respectively, as shown in FIG. 1, are designed to be as short as possible. These short overhangs make it difficult to locate a muffler 7 parallel to the longitudinal direction of the vehicle under the rear overhang 6, because of the limited size of the rear overhang 6. Hence, in the midship engine rear wheel drive-type sports cars, the muffler 7 is positioned laterally across the vehicle, as shown in FIG. 9. The reference FWD in FIG. 9 designates a forward direction in the vehicle.
It is desirable to have large luggage compartments in all cars, including small sports cars. However, the lateral positioning of the muffler 7 across the vehicle body tends to limit the permissible size of a luggage compartment. Hence, the cylindrical muffler is maintained to be as small as possible for space purposes, while large enough to attenuate exhaust noise from the engine. This permits a floor 16 of the luggage compartment 15 to be as close to the ground as possible.
In a midship engine rear wheel drive-type vehicle, as shown in FIG. 1, the engine 3 is mounted at a position between the rear axle shaft 1 and the passenger seat 2. The engine 3 is transversely mounted, as shown in FIG. 9, because of the limited longitudinal length of the rear overhang 6. In a vehicle having a transversely mounted engine, the muffler 7 has been mounted onto the vehicle body through resilient members 12 and 13, which are flexible upwardly and downwardly with a small amount of force. FIG. 9 shows that the resilient members 12 and 13 are in the form of disc plates. The resilient members 12 and 13 are located on the same horizontal plane. One end of each of the members 12 and 13 is fixed to longitudinal ends 10 and 11 of the muffler 7, respectively. A second end of each of the members 12 and 13 is fixed to side members 18 and 19, respectively. The resilient members 12 and 13 are relatively thin in the direction in which they are upwardly and downwardly flexible and therefore bend quite easily in this direction (the upward and downward displacement corresponds to the arrows V--V in FIG. 9).
When the engine 3 is running, it rolls about the axial line N--N of a crank shaft (not shown in drawings) in the direction designated by an arrow C in FIG. 9. In a vehicle having a longitudinally mounted engine, as shown in FIG. 7, the distance "l" between the axial line of the crank shaft N--N and an axial line of the exhaust pipe 8 is small. While in a vehicle having a transversely mounted engine, as shown in FIG. 8, the distance "L" between the axial line N--N of the crank shaft and a tail end of the exhaust pipe 8 is large. Hence, in the vehicle having a transversely mounted engine, the exhaust pipe 8 amplifies the amplitude of the vibration of the engine roll (the vibration in the direction of the arrows C--C about the axial line N--N in FIG. 8). The amplified engine roll causes the muffler 7 to vibrate upwardly and downwardly with great amplitude. To attenuate this upward and downward vibration of the muffler 7, resilient members similar to the resilient members 12 and 13, have been utilized.
According to a known exhaust support system shown in FIG. 9, the resilient members 12 and 13 are designed to be thin in the upward and downward vibration direction thereof. When the vehicle body is upwardly and downwardly vibrated, because of the rough road conditions, the muffler 7 and a catalytic converter 14 also upwardly and downwardly vibrate. The muffler 7 and the catalytic converter 14 individually and collectively have a considerable weight, resulting in the amplitude of the upward and downward vibrations becoming considerable.
Further, when the vehicle body is upwardly and downwardly vibrated due to rough road conditions, the engine 3 does not always vibrate in phase with the muffler 7 and the catalytic converter 14. The engine 3 is mounted by an engine mount (not shown in drawings), which fixes the engine 3 to the vehicle body. The engine mount is hard in comparison to the resilient members 12 and 13. Hence, when the vehicle is upwardly and downwardly vibrated, the engine itself does not generate large upward and downward vibrations. Therefore, when the vehicle is upwardly and downwardly vibrated, a relative displacement occurs between the engine 3 and an exhaust device, such as the muffler 7. Further, a vibration absorbing device 9 is provided to absorb the vibrations of the engine 3. The vibration absorbing device 9 is limited in the amount of vibrations that it can absorb because of its limited size. Therefore, the vibration absorbing device 9 can be damaged by any substantial relative displacement between the engine 3 and the exhaust device.
Additionally, when the muffler 7 is heated from the engine exhaust, the thermal expansion of the muffler 7 in its longitudinal direction becomes significant. However, because both ends 10 and 11 of the muffler 7 are restricted by the resilient members 12 and 13, thermal expansion of the muffler 7 in its longitudinal direction (the direction of the arrow P in FIG. 9) is restricted. The restriction of the thermal expansion results in a compressive force being generated within the muffler 7. If the strain upon the muffler 7 caused by the compressive force is present for a long period of time, the muffler 7 might become plastically deformed, even though the resilient members 12 and 13 absorb a portion of the thermal expansion of the muffler 7. The resilient members 12 and 13 are located parallel to the direction of the arrow P in FIG. 9, which is parallel to the potential longitudinal thermal expansion of the muffler 7. This results in the resilient members 12 and 13 having a high stiffness in the direction of the arrow P in FIGS. 9 and 10. Hence, the resilient members 12 and 13 can absorb only a small portion of the longitudinal expansion of the muffler 7.